This invention generally relates to remote signal communication systems, and more particularly to a method of controlling the signal sensitivity of a remote signal communication system during passive authentication.
A variety of remote signal communication systems are used in vehicles. Radio frequency (RF) signals have become a communication mode of choice in a number of systems of this type. Examples include remote keyless entry systems (RKE) and passive entry and starting systems (PASE). Such systems typically include a handheld transmitter, such as a key fob or “smart card”, which provides a signal to a receiver module located on the vehicle. The receiver module actuates a vehicle system in response to transmissions received from the transmitter. The receiver module may unlock a vehicle door in response to transmissions received from the transmitter where the system controlled by the transmitter is a RKE system, for example. In another example, the doors of a vehicle are automatically unlocked where the transmitter is within a predefined range, such as approximately three meters, from the vehicle and the system controlled by the transmitter is a PASE system.
One challenge facing designers of typical RKE systems is increasing the range in which the transmitter and the receiver module components of the RKE system will satisfactorily operate. Typically, the receiver module is provided with an external antenna, such as an antenna encased in the rear view window of a vehicle, to increase the distance that the receiver module may effectively respond to transmissions emitted by the transmitter. In addition, a low noise amplifier (LNA) circuit is typically provided within the receiver module to amplify the incoming signal received by the receiver module where the operating range of the RKE system is required to be large.
Disadvantageously, use of external antennas and LNA circuits to increase the operating range of an RKE system may result in a non-functioning PASE system. For example, the external antenna receives an increased signal which includes increased noise associated with that signal. In addition, the LNA circuit amplifies the signal including the noise associated with the signal. The combination of the receipt of an increased signal by the external antenna and the amplification of the increased signal by the LNA circuit may cause interference with the RF frequency carrier signal that the PASE system is operating on that is so extreme that the PASE system is rendered non-functioning. This results in the necessity of the vehicle owner to enter and start the vehicle in a traditional manner such as by using a key. In the alternative, the external antenna may be unplugged so as to not interfere with the PASE system. However, by unplugging the external antenna, the RKE system performance may be severely diminished.
Accordingly, it is desirable to provide both external antenna and LNA circuit control during passive authentication such that both an RKE system and a PASE system may be utilized simultaneously without decreased performance by either system.